High Quality Carbon Nanotubes on Conductive Substrates Grown at Low Temperatures

For carbon nanotubes (CNTs) to be exploited in electronic applications, the growth of high quality material on conductive substrates at low temperatures (<450 °C) is required. CNT quality is known to be strongly degraded when growth is conducted on metallic surfaces, particularly at low temperatures using conventional chemical vapor deposition (CVD). Here, the production of high quality vertically‐aligned CNTs at low substrate temperatures (350–440 °C) on conductive TiN thin film using photo‐thermal CVD is demonstrated by confining the energy required for growth to just the catalyst using an array of optical lamps and by optimizing the thickness of the TiN under‐layer. The thickness of the TiN plays a crucial role in determining various properties including diameter, material quality, number of shells, and metallicity. The highest structural quality with a visible Raman D‐ to G‐band intensity ratio as low as 0.13 is achieved for 100 nm TiN thickness grown at 420 °C; a record low value for low temperature CVD grown CNTs. Electrical measurements of high density CNT arrays show the resistivity to be 1.25 × 10^‐2 Ω cm representing some of the lowest values reported. Finally, broader aspects of using this approach as a scalable technology for carbon nanomaterial production are also discussed.     

Hydroxide Is Not a Promoter of C2+ Product Formation in the Electrochemical Reduction of CO on Copper

Highly alkaline electrolytes have been shown to improve the formation rate of C₂₊ products in the electrochemical reduction of carbon dioxide (CO₂) and carbon monoxide (CO) on copper surfaces, with the assumption that higher OH^? concentrations promote the C?C coupling chemistry. Herein, by systematically varying the concentration of Na⁺ and OH^? at the same absolute electrode potential, we demonstrate that higher concentrations of cations (Na⁺), rather than OH^?, exert the main promotional effect on the production of C₂₊ products. The impact of the nature and the concentration of cations on the electrochemical reduction of CO is supported by experiments in which a fraction or all of Na⁺ is chelated by a crown ether. Chelation of Na⁺ leads to drastic decrease in the formation rate of C₂₊ products. The promotional effect of OH^? determined at the same potential on the reversible hydrogen electrode scale is likely caused by larger overpotentials at higher electrolyte pH.     

Integrated load‐based power saving for BS and MSS in the IEEE 802.16e network

In our previous work, the limitation of standard type I and II power saving in IEEE 802.16e was discussed, and the idea of load‐based power saving (LBPS) was proposed for better power‐saving efficiency. LBPS measures traffic load and adaptively generates proper sleep schedule for the current load. Three LBPS schemes have been proposed for mobile subscriber station (MSS) power saving. In this paper, base station (BS) power saving is taken into consideration, and our previously proposed LBPS schemes, are extended and revised to integrate both BS and MSS in sleep scheduling. Two strategies of integrated power saving, MSS first and BS first, each with associated LBPS schemes are proposed in the paper. A three‐staged concept combining the proposed strategies is also presented to make the best of integrated power saving. A simulation study shows that the proposed schemes can effectively achieve high power‐saving efficiency for both BS and MSS. Copyright © 2013 John Wiley & Sons, Ltd.     

Enhancing performance of nonvolatile transistor memories via electron‐accepting composition in triphenylamine‐based random copolymers

With the rapid advances in organic memory, organic field‐effect transistor (OFET) memory has been recognition of the value over the past few years. Although the functional polymer with the Donor‐Acceptor (D‐A) structure has been widely investigated, little research has been carried out to clarify the relationships among D‐A structure of the polymer, capability of charge‐transfer, and memory performance. Here, we report the nonvolatile memory characteristics of pentacene‐based OFET memory using random copolyimides, poly[4,4′‐diaminotriphenylamine‐hexafluoroisopropylidenediphthalimide‐co‐4‐(N,N‐bis(p‐aminophenyl)amino)‐4′‐nitroazobenzene‐hexafluoroisopropylidenediphthalimide) (PI(TPA‐6FDA‐DACx)), with feeding ratios of DAC to TPA set as x (where x = 0,10, 30,50,70,100). The OFET memory performance based on the molar ratio of DAC to TPA equal to 30:70 represents the best results with the proper charge mobility, on/off current ratio, and memory window. Intriguingly, the memory performance can be enhanced by introducing more D‐A monomer in polymer electrets, yet the concomitant inferior growth of pentacene decreases the charge mobility, attributed to the intrinsically destructive arrangement of polymer backbone. Our conclusion points out the importance of polymer arrangement and capability of charge‐transfer to the OFET performance and memory characteristics. The comparable results can also be applied for advanced OFET memory devices. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1113–1121     

Application of Two Hopfield Neural Networks for Automatic Four-Element LED Inspection

A system for the automatic inspection of LED wafer defects is proposed to detect defective dies in a four-element (aluminum gallium indium phosphide, AlGaInP) wafer. There are over 80000 dies on an LED wafer. Defective dies are typically visually identified with the aid of a scanning electron microscope. This process involves dozens of operators or engineers visually checking the wafers and hand marking the defective dies. However, wafers may not be fully and thoughtfully checked, and different observers usually find different results. These shortcomings lead to significant labor and production costs. Therefore, a solution that consists of two Hopfield neural networks, of which one is used to identify the LED die regions and the other is used to cluster the die into three groups, is proposed to facilitate the detection of defective dies in wafer images. The experimental results show that the proposed method successfully detects defective dies in a four-element wafer.     

The Effect of Nanoscale Confinement on the Collective Electron Transport Behavior in Au Nanoparticles Self‐Assembled in a Nanostructured Polystyrene‐block‐poly(4‐vinylpyridine) Diblock Copolymer Ultra‐thin Film

This study involves the collective electron transport behavior of sequestered Au nanoparticles in a nanostructured polystyrene‐block‐poly(4‐vinylpyridine). The monolayer thin films (ca. 30 nm) consisting of Au nanoparticles self‐assembled in the 30‐nm spherical poly(4‐vinylpyridine) domains of an polystyrene‐block‐poly(4‐vinylpyridine) diblock copolymer were prepared. From the current‐voltage characteristics of these thin films, the collective electron transport behavior of Au nanoparticles sequestered in the spherical poly(4‐vinylpyridine) nanodomains was found to be dictated by Coulomb blockade and was quasi one‐dimensional, as opposed to the three‐dimensional behavior displayed by Au nanoparticles that had been dispersed randomly in homo‐poly(4‐vinylpyridine). The threshold voltage of these composite increased linearly upon increasing the inter‐nanoparticle distance. The electron tunneling rate constant in the case of Au nanoparticles confined in poly(4‐vinylpyridine) nanodomains is eight times larger than that in the randomly distributed case and it increases upon increasing the amount of Au nanoparticles. This phenomenon indicates that manipulating the spatial arrangement of metal nanoparticles by diblock copolymer can potentially create electronic devices with higher performance.     

A Review of Reliability Research on Nanotechnology

Nano-reliability measures the ability of a nano-scaled product to perform its intended functionality. At the nano scale, the physical, chemical, and biological properties of materials differ in fundamental, valuable ways from the properties of individual atoms, molecules, or bulk matter. Conventional reliability theories need to be restudied to be applied to nano-engineering. Research on nano-reliability is extremely important due to the fact that nano-structure components account for a high proportion of costs, and serve critical roles in newly designed products. This review introduces the concepts of reliability to nano-technology; and presents the current work on identifying various physical failure mechanisms of nano-structured materials, and devices during fabrication process, and operation. Modeling techniques of degradation, reliability functions, and failure rates of nano-systems are also reviewed in this work.     

High Tg and high organosolubility of novel unsymmetric polyimides

A series of new polyimides (PIs) containing di‐tert‐butyl side groups were synthesized via a polycondensation of 1‐(4‐aminophenoxy)‐4‐(4‐amino‐2‐methylphenyl)‐2,6‐di‐tert‐butylbenzene ( 3 ) with various aromatic tetracarboxylic dianhydrides. The novel unsymmetric PIs exhibited a low dielectric constants (2.78–3.02), low moisture absorption (0.53–1.35%), excellent solubility, and high glass transition temperature (308–450 °C). The PI derived from the new diamine and the very rigid naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA) was soluble in N‐methyl‐2‐pyrrolidone, chloroform, m‐cresol, and cyclohexanone. The unsymmetric di‐tert‐butyl pendent groups significantly enhance the rotational barrier of the polymer chains; thus these PIs had high T_gs. The ¹H NMR spectrum of the diamine 3 revealed that the protons of 4‐aminophenoxy moiety are not chemical shift equivalent. This is because the steric hindrance of the bulky di‐tert‐butyl groups prevents the benzene ring of 4‐aminophenoxy moiety from rotating freely. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2443–2452, 2009     

A compact RCS formula for a dihedral corner reflector at arbitraryaspect angles

A compact closed-form formula for the RCS of a perfectly conducting right dihedral corner reflector at arbitrary aspect angles is presented. The approach is based on a combination of ray tracing, physical optics (PO), and the physical theory of diffraction (PTD). There is good agreement between the results obtained using the closed-form formula and those obtained by the shooting and bouncing rays (SBR) technique     

Scattering from a cavity-backed slit in a ground plant-TE case

Two-dimensional transverse electric wave scattering from a cavity-backed slit in a ground plane is analyzed by R.F. Harrington and J.R. Mautz's (1976) generalized network formulation. The admittance matrix of the cavity or arbitrary shape and medium is obtained by the finite-element method. A variational equation for the cavity problem is established and then discretized to a matrix equation. An efficient algorithm using the modified frontal-solution algorithm is developed to solve the matrix equation. The solution is manipulated to get the admittance matrix of the cavity. The computed admittance matrix is added to the radiation admittance matrix of the equivalent magnetic current on a ground plane and is used to solve for the equivalent magnetic current on the slit. Numerical results for trapezoidal and coated rectangular cavities are included